i put the second a/c in mine to have a spare and not be without. decided on the heat pump also to save on the propane. cost wasn't much different than an a/c alone.
the first season after installing, we used both features on the first trip out. more of the novolity of running the heat sense we would have put up with the morning chill rather than run the heat for a few degs.
on the same trip, we encountered 115 deg days and one unit would not keep up. was glad we had it. a couple yrs earlier, in the same area, one unit didn't quiet keep up when the outside temp was around 100.
most of the time, we use the unit at night mainly to block outside noise.
one thing ur going to find abt the heat pump, it doesn't work below abt 40 deg. i don't believe it went on heat strip until the outside temp got closer to 35. (mine has a heat strip backup which puts abt 1/3 to 1/2 what the heat pump does).